Power line carrier current system



July 4, 1933- k c NEBEL 1,917,052

POWER LINE CARRIER CURRENT SYSTEM Filed Aug. 10, 1929 2 Sheets-Shet 1 DEM LPF

HHH HHH \HHI HUN Q mm mm N E? @MQR RPF EZ/V. NEBEL BY ATTORNEY July 4, 1933. c N, NEBEL 1,917,052

POWER LINE CARRIER CURRENT SYSTEM Filed Aug. 10, 1929 2 Sheets-Sheet 2 REC LPF

a) mm mm um mm II E II 3 r. \i n lNVENTUR' CiN/VEBEL A TTURNE) have selective calling circuits for operatingi selectorsat the signal stations by GOdGSIg-r Patented 4 ':19 3 L s I ceived. I s V Another object of the invention is topro-Tj vide a carrier-current telephone system em .CHARLESKINEBEIQQOF NEWARK, NEW asitsninfnssienon. ro iannnrnnsrnoivn LABO- RAroRrEs, rnoon ron-n'rnn, on NEFHYQRK N. Y., noonronarron QE'NEW, YQBK' 1 "towns LINE onnarmtoonnfsnr sys'rn vr Application filedAug ust 1o, i929; serial No. 384,878. I

Thisinvention relates to selective lcalliin'g circuits and particularly to selective calling circuits for power-line carrier-current tele-- phone systems.

One object of the invention is to'provide a carrier-current telephone system with selec5 ive callingcircuits that shall-befoperatedby code signals of carrier current and "be rendered inoperative when carrlercurrent modue lated with voice frequency currents is're ploying modulated carrier currentlfor com:

mui'aication between station's with selective. calling circuits that shall, be operativef for calling purposes when unmodulated impulses. H p I v carrier current telephone system whereinthe carrier waveand both side bands are trans- 'mitted; during communication between stag" tions; prljovisi'on'is" made in the tran'smitting 7 channel at the calling stationito transmit. a -j codesignal of unmodulated carrier current" for operating-"a callselector ata calledstation. At 1 the foal-led station two amplifier tubes in push-pull relationship are connected;

of carrier currentare beingtransmitjted and A, further object of the inventi'onis to pro vide a' powenline carrier current systemem ploying modulated carrier current for communication between signal stat1ons-that shall Lnals of unmodulated ca-rriercurrent' and auxtransmitted over the power line, t In power-line carrier-current telephones v Y I M v it'or; Provision lsmade 01" blOCklIlgand p iliary circuits for rendering the calling circuits inoperative for opera-tmgthe'selectors when -modulated carrler current sbe ng' s stems a plurality 'ofsignal stations are con modulated carrier current and provision is 7 directions by the same carrier wav'efl Onfej system which is'employed to disclosethe'in venti on is disclosedand claimed in the patent made whereby each station mayfselectively' call any other. stat-ionover the power line.

In the systems employed to' disclose" this" s y a I "tube 18 provided mrthe receiv ng jchannellfor invention communication is eflecte dfi'n both to CL'N. Nebel, No; 1,733,553; dated October 29, 1929, fA second-system which is employed to disclose; the invention is disclosed and 2 claimed in the application of J. DfSarro's,"

ing communicating between stations; In. the

above mentioned application J;.'D Sarros,

the same carrier wave is employed for transmission in .both -'directions and the carrier cording to invention by transmitting a code signal of unmodulated carrier current or carr-ier current modulated with a second wave and"bothcside bands are transmitted vover the "power l ne .durm'g jjcommunication carrier'current to the called stallion. Pro-' vision is made-Ito prevent operation of the calling circuit when any carrier current modulated with voice frequency" currents is being transmitted over the power lmei.

in applying this invent onto a power line to the receivingfchannel so astoibe supplied with vthe high; frequency; modulated or un modulated carrier current transmitted over the 1 power line; :Thefloutput f circuits of the two amplifierftubes' in push-pull relationship a are connected to Qa'thermionic rectifier which controls the operation ofa'suitable'calljselem I venting operation of the twoamplifier tubes exceptflwhen unmodulated carrier current free from any mo'dulation with 'voice frequency currentis received over the power line, 7 v

In the system u'nder'considerat on wherein the carrierfwav'e and" both slde'bandsare transmitted over thepower line,a,detectorj v i obtaining the-voicefrequency currents which have been modulated with the carrier wave;

The" voice [frequency currents from the out-I suitablelow -p assjfilterand by means of an auxiliary control, circuit comprising a the'r-Z mionic amplifier appl a; negative blocking lipotentialto the grids of theiabove mentioned two amplifier tubes in f'pus'hep'ull relation; ship toeach other.) Thus whatever modu-H lated currents are received overi the power, line, the thermionicamplifier tubes controllingfthe selector :arejblocked to prevent any lector would be operated operation of the selector whatsoever. Accordingly, calling of the distantstation can only be effected by transmitting code signals of unmodulated carrier current free from any modulation with voice frequency currents.

If a single side band is transmitted over the power line for communication purposes as in the above mentioned patent to C. N. Nobel, No. 1,733,553, selective calling in accordance with this invention is effected by transmitting a code signal comprising impulses of the first carrier current modulated with. the second carrier current. In a system of the type disclosed in the application of C. N. Nebe Serial No. 282,810, two demodulators are provided in the receiving channel of each signal station. The output circuit of the first demodulator contains the lower frequency carrier wave and modulated products of this lower frequency carrier wave with voice frequency currents. The two amplifier tubes in push-pull relationship which are connected to a rectifier for operating a selector in accordance with this invention are connected to the output circuit of the first demodulator tube in order to be operated by the lower frequency carrier wave. l Vithout ad.- ditional. blocking means it is apparent the sely impulses of the lower frequency carrier wave or by impulses of the lower frequency carrier wave modulated with voice frequency currents.

In order to prevent operation of the selector when communication between stations is being effected and voice frequency currents modulated with the low frequency carrier appear in the output circuit of the first demodulator, an amplifier and a rectifier tube are connected to the output circuit of the second demodulator. The amplifier tube and the rectifier tube which are operated by the voice frequency currents in the output circuit of the second demodulator apply a negative blocking potential to the grids of the two tubes in push-pull relationship which control the operation of theselector. Accordingly the selector at a called station in the system of the type under consideration can only be operated when impulses of carrier current free from any modulation with voice frequency currents is received at the called station.

In the accompanying drawings Figure 1 is a diagrammatic view of a sig nal station provided with calling circuits constructed in accordance with the invention.

Figure 2 is a diagrammatic view of a modification of the invention.

Referring to Fig. 1 of the drawings, a signal station is shown which is adapted to be connected to a power line carrier current system of the type disclosed in the patent to C. N. Nebel, No. 1,733,553. The signal station is particularly adapted for operation in a power line carrier current system wherein double modulation is effected at the transmitting station and only one side band of the modulation products is transmitted to the distant station.

An operators telephone set 1 is connected by a transformer 2 and a hybrid coil 3 to a transmitting channel 4 and receiving channel 5. The hybrid coil 3 is provided with the usual balancing network 6.

The transmitting channel comprises a first modulator 7 which is preferably of the then mionic type disclosed in the above mentioned patent to C. N. Nobel and a second modulator comprising thermionic tubes 8 and 9 con nected in push-pull relationship to each other. An oscillator 10 which is preferably of the thermionic type is connected to the first modulator 7 by means of transformer 11 for supplying a carrier current of relatively low frequency to be modulated. with the voice frequency current supplied to the first modulator tube. A second oscillator 12 is connected by transformer 13 to the input circuits of the thermionic tubes 8 and 9 which comprise the second modulator. The second oscillator 12 supplies the second modulator with a carrier current of relatively high frequency. A. band pass filter 14c in the output circuit of the first modulator 7 is connected by a transformer 15 to the input circuits of the thermionic tubes 8 and 9. The output circuits of the thermionic tubes 8 and 9 are connected by ransformer 16 and a filter 80 to a power amplifier 17. The power amplifier 17 is connected in the manner disclosed in the above mentioned patent to C. N. Nobel to the high tension power lines.

A code selector key 18 of any suitable type such, for example, as the master impulse transmitting device disclosed in the patent to J. C. Field, No. 1,354,814, dated October 5, 1920, is provided for operating a relay 19. The relay 19 is provided with three armatures 20, 21 and 22. The armature 20 in the released position engages a contact member 23 and in the operated position engages a contact member The armature 21 in the released position engages a contact member, and in the operated position engages a contact member 26. The armature 22 in the operated position engages a contact member 27 for short-circuiting a resistance element 28.

When relay 19 is deenergized and the armatures 20 and 21 engage with the contact members 23 and 25, the first modulator 7 is connected through the band pass filter 14 and transformer 15 to the input circuit of the second modulator. Upon operation of the relay 19 from a battery 29 by the selector key 18, the armatures 20 and 21 engage the contact members 24- and 26 for connecting the first oscillator 10 through a transformer member 27 for short-circuiting there'sistance 30' to the input circuit of the second' modulator. The armature 22' engages the contact element 28.

The resistance element- 28 is part of the duplex control circuitsshown-and-described,' I p 1 mitted to the second I modulator, comprising 7 in the above mentioned patentito G. NLNebel,

No. 1,733,553. When the receiving-channel is in service or the station isidle,*a'potential is impressed upon resistance element28= for placing a'blocking negative potential on the grids of the thermionic tubes 8 and 9; The placing of a shunt circuit across the resistance element 28 insures against any blocking of the second 'modulator when: a

I calling signal is being transmitted The du plex control circuits'for impressing potentials on the'control resistance28 is not a part of the present invention and a detailed description thereof is deemed unnecessary. 7

Thereceiving channel 5 comprises a first demodulator 31, a bandpass filter32, a second demodulator 33, anda low pass filter 5 34'which is connectedby thexhybrid coil 3 and the transformer 2 to the operators telephone set 1. The demodulators 31 and133 and the filters 32. and 34 aresimilar in con:

struction and operation toxlike parts shown C; ,N. Nebel,

and described in the patent to I A selector 354: provided for operatin a suitable call-signal (not shown). wo thermionic tubes, 36 and 37 which are con-' 1necred-in push-pull relationship and a rec tifier thermionic vtube 38 are provided] for operating the selector'35. The input circuits former 40 is provided for connecting the amv j were impressed upon the resistance element' 45,: such icurrent' 'woulcl effect the operation I offtheselectorf3'5by meansof the musselof the amplifier 'tubes 3'6'and 37 are connected by a transformer 39 to the receiving channel 5"at .a point between-th e band pass filter 32 and" the second demodulator 33. A'tran sr plifier tubes 36 and37 tothe rectifier38 tion. The amplifiertu-be4l i'sconnect ed by 'a' tr ansform'er 43 to the receiving channel 5 -at a point beyond the low pass filter "34 7 so as to be operated by voice frequencycurrents. Therectifier 42 is connected Ito the amplifier tube 4l-by atransformer 44' and impresses a potential across a-resistance ele ment 45 in the input circuits ofthe 'ampli fier tubes 36and 37. The resistance element 45 serves to impress a negative blockingpoi 'tential on the grids 'of the amplifier "tubes 36 and 37 to prevent the operation of the" selector 35 when carrier currents modulated with voice frequency currents-are received;

overthe', power line; A condenser 46 is convnected across the resistance element 45 for' smoothlng out anyripples 1n theoutput c1rcuit of the rectifier;

' In the operation of the signal station shownlectedby the band pass filter 14 and trans.

thethermionic" tubes 8 a nd 9 r The tubess and 9 Inodulate' the side band received from f the first' modulator with a carrier wave of Z 1 relatively high frequency received from the.

oscillator 1 The {output from the second modulator passes through'a filter forIsethe power amplifier 17 to the power line. 'l/Vhen it is desired; to selectively call'ar distant station, the key '18 'is operated for controlling-the relay 19 in accordance with a code signal: The operation of the relay, 19 selectively connects the oscillator 10 with lectin'g one side band which is passed" through I the input circuit of "the second modulator to transmit a1 code 1 signal of impulses The code signalQtransmitted over"thepower' line consists offone "side bandobtained from second" oscillator.

from the second modulator and a'shuntc-ircu-it -is connected across the resistance element 28 so' as toinsure against impressing any negativeblocking potentialonlthegrids y of the'modu-latortubes1 8 and'9 by the duplex control: circuitsdisclosed in the patent to :G.N. Neb'el, N0..1,7ee,55e.. I

YVhen communication is being "effected be tweentwostations, the two amplifier tubes; 7 '36 and 37. are supplied by the "transformen 39 connected tothe output of the band pass filter 32' with current of the frequency of modulating the'carriercurrentfrom'thefirst oscillator with'ithe carrier. current from the At this time, as before set forth, the firstfmodul'ator is dis'connected the oscillator 10.; If no blocking potential 38. -At the same time, however, the amplicurrents from the output of the low pass V filter 34.:-The"outputfromfthe amplifier tube 41 is rectified by the tube 42., The rec-' grids of the two amplifier tubes 36 and. 37. a

Thus during communicationibetween the I two stations, means are provided for insur-f gainst any operationof the selector at "any station. 1 i

calling mpulses or a side bandproducedflby modulating-the carrier. wave from; a the first oscillator 10 with-the carri-er'wave. V fromthe secondoscillator 12, are received in a tifierimpresses blocking potential on the ing the receiving'channel v5 the amplifier tubes 36 blocking potential on the grids of the amplifier tubes 36 and S7. e

In Fig. 2 of th drawings a diagrammatic receiving circuit is shownfor use in a system of the type disclosed in the application of J. I). Sarros, Serial No. 38t,8?6, filed August 10, 1929. In a system of this type communication between two stations on the power line is effected by transmitting the carrier wave and both side bands and se lective calling is effected by transmitting code signals of the carrier wave unmodulated withany voice frequency currents.

The receiving channel shown in Fig. 2 of the drawings comprises a band pass filter 50, which selects the carrier wave and the side bands which are characteristic of the system. Ihe band pass filter 50 is connected to a detector 51 which is preferablyof the thermionic type. The output circuit of the detector tube is connected through a low pass filter 52 to the operators telephone set 53. The means connected to the receiving channel for operating the selector is similar in construction and operation to like means shown in Fig. 1 of the drawings. Accordingly, the same reference characters will be used in Fig. 2 to indicate like parts shown in Fig. 1 of the drawings.

When carrier current impulses free from any modulation. with voice frequency currents are received, the amplifier tubes 36 and 37 and the rectifier 38 are operated for effecting operation of the selector 35. However, if any carrier current modulated with voice frequency current is received, the amplifier tube 41 and the rectifier 42 are operated for impressing negative blocking potential on the grids of the tubes 36 and 37 to prevent any operation of the selector.

Modifications in the systems, and in the arrangementand the location of parts may be made within the spirit and scope of the invention. and such modifications are intended to be covered by the appended claims.

What is claimed is:

1. In a power-line carrier-current signal system, a high-tension power line,a plurality of signal stations connected to said power line, means for communicating in opposite directions between stations by carrier current of one frequency modulated with voice frequency currents, control means for selec tively calling a station by transmitting code signals of said carrier current free'from modulation with voice frequency currents, and means at said stations responsive to the current employed for communication between stations for preventing operation of said control means during communication beconnected to said line, means for communieating in opposite directions between stations by a carrier current of one frequency modulated with voice currents, call means at each station responsive to a codesignal of said carrier current, and means at each station responsive to carrier current modulated with voice frequency current for preventing operation of said call means. i

3. In a carrier-current signal system, a transmission line, a plurality of signal stations connected to said line, means for communicating in opposite directions between stations by carrier current of one frequency modulated with voice frequency currents, calling means at each station for selectively calling a distant station by transmitting a code signal of said carrier current free from modulation with voice frequency currents, selector means at each station responsive to carrier current signals free from modulation with voice frequency currents, and meansat said stations responsive to the current employed for communication between stations for preventing operation of said selector means during communication between stations. r

4. In a carrier-current signal system, a signal station, means at said station for'cemmunicating with another station by modulated currents, selector call means at the Sta tion responsive to carrier currentimpulses free from modulation with voice frequency currents, and means responsive to carrier current modulated with voice frequency currents for preventing operation of said selector call means.

5. In a carrier-current signal system, a signal station, means at said station for communicating with another station by modulated currents, cal means at said station, control means responsive to carrier current for operating said call means, and means responsive to carrier current modulated with voice frequency currents for preventing operation of said control means. I I v 6. In a carrier-current signal system, a

transmission line, a plurality of signal stations connected to said line, means for effecting communication in opposite directions between two stations by carrier current of one frequency modulated with voice frequency currents, means at each station for transmitting code signals of said carrier current free from modulation with voice frequency currents to selectively call another station, selectors at said stations, control means at each station responsive to a code signal of carrier current free from modulation with voice frequency currents for operating a selector, and means responsive to carrier current modulated with voice frequency currents for pr ventin operation of said con-trol means.

7. In a power-line carrier-current signal system, a power line having a plurality of signal stations connected thereto, means at said stations for effecting communication in opposite directions 'bycarrier current of one frequency. modulated with voice frequency currents, means at said stations for calling by said carr er current free from modulation with voice frequency currents, selectors at said stations, control means at said "stations lated carrier current, call means at said sta-' responsive to carrier current free from modulation with voice frequency currents fo r'opera ating said selectors, and means responsive to carrier current. modulated with voicefrepreventingoperation of said control means. 1

8. In a power-line carrier-currentlsignal system, a power line having a plurality of tions, control means at said stations respon-g sive to'carrier current for operating said call means, and meansat said stations responsive to modulated carrier. current for preventing operation of said control means. I 1

9. In a carrier-current signalsystem, 'atransmission line, a signal stationconnect-ed to said line, means at said station forxconn municatingover said line by modulated car rier currents, a selector at saidstation, means; comprising a three-element thermionic am-t plifier tube for operat ng sald selector byimpulses'of carrier current received at said. station, and means operated when modulated currents are received at said stationfor applying a negative blocking potential-to the,

grid of said amplifier tube topreventopera-t I tion of saidselector;

10. In a carrier-current signalsystem em I ploying the same carrier current wave for transmission in both directions, a'transmission line, a signal station having a transmitting and a receiving channel connected'to I said line, means in said transmitting channel for transmitting 'modulated carrier waves for commuicating with another station and for transmitting a code signal of unmodulated carrier current to selectively call' another station, means in said receiving channel for demodulating the currents employed in com- 7 municating'with a distant station, aselector,

con-trol means .governed by the carrier current transmitted to said receiving channel .for operating said selector, and mea'ns operated by the demodulation products in the receiving channel for preventing operation .of the selecm by said control means whenmodulated carrier current isreceivedf v I H 11. In a carrier-current signal system, a

' signal station having a receiving channel, two series related demodulatmg means and a.

low pass filter in said channel, a selector at said station, control means governed by the h output fromthe first demodulator for operating said selector, and means connected to said from the second demodulator for operation of saidcontrol means. I 12. In a power-linecarrier-current system,

a power line carrying highvoltage low frefilterand operated low frequency output preventing:

quen'cy power currents, a signal station havmg a receiving channel connected to said? power lme,'two series connected demodulator tubesin said receiving channel and adapted to demodulatecurrents which haverbeen" twice modulated, a selector, control means for operating'saidsel'ector by the output from the firstdemodulator, and means operated by 7 the low frequency, output from the second ide= modulator for control means. I

.quency power currents, .a signal station-con nected to said power line, means at said stationforcommunicating with another station by high frequency. modulated currents, a

preventing operation of said V 13. Ina power-linecarrier-current'system, a powerline carrying high-voltage low fre- Y selector'at said station, control means responsive to"h1gh-frequency vcarrier-current 1 for :operating said selector, and means responsive to modulated carrier current for preventing operation-of said control means.

1a. Ina carrier current signal system em- Iploying the samecarrier wave for communication in opposite directions, asignal station" havinga transmitting and a receiving ichan-- nel, two series-related modulators and two oscillators insaid transmitting channel for effecting two modulating operations with the voice frequency currents during communica- 1 tion with a distant station,'means for modu} lating current from the first oscillator with current from the second oscillator-for transmitting a code signal of one side band, two demodulators and a low pass filter se riesconnected in said receiving channel, a selector at said station, control means operated by the outputfrom the first demodulator for operating said selector, and means connected to the output circuit'of said-filter and operated by the low frequency output from'the seconddemodulatorfor preventing operation or; said control means when'modulated currents are received.

1 5. In a carrier Current signaling system, a signal station, means at said station for communica-ting with a second station 'by'modulated currents, call means'at said second sta- 't1on,'control means at said second. station rei 120 sponsive to carrier currentreceived from said first station for operating said call means,

and means at said secondstation responsive v to modulated current received from saidfirst station forpreventing operation of said icontrol means.

In-jwitn'ess whereof, I hereunto subscribe myjname this 9th day of August, 1929.

. CHARLES N N EBEL. 1 

